Early developmental patterning sets the stage for brain evolution

Abstract

The evolution of brain structure and function has long fascinated biologists. This fascination was initially prompted by the observation that allometric relationships exist between the size of the brain—or brain region—and body size across a wide range of vertebrates (1). Besides random drift, two main ideas have been advanced to explain how brains evolve, and both have found considerable support. From a purely adaptationist point of view, selection on a specific set of behavior patterns or sensory specializations is thought to result in “mosaic” changes in only the brain regions that mediate these processes (2). In contrast, selection on any single brain region would cause the brain to change as a whole unit owing to developmental constraints and processes that regulate the formation and growth of a range of brain regions overall (3).